1. Field of the Invention
The invention relates to an intake manifold used in an internal combustion engine or the like mounted in a vehicle such as an automobile, for example.
2. Description of the Related Art
The engine to be mounted is provided with an intake manifold for supplying air to a combustion chamber. The intake manifold is such that a plurality of intake passages which are connected to a plurality of intake ports of the internal combustion engine are formed integrated with a surge tank which is disposed upstream of those intake passages and to which an outside air intake path is connected.
An intake manifold is provided with a gas introduction hole and an intake air negative pressure outlet hole. The gas introduction hole is provided for introducing gas containing water vapor or oil content in the form of mist, such as EGR gas (re-circulated exhaust gas), purge air from a canister, or blow-by gas in the crankcase, or the like. The intake air negative pressure outlet hole is provided for applying intake air negative pressure within the surge tank to a brake booster or the like, for example.
The gas introduction hole and the intake air negative pressure outlet hole are preferably arranged in locations that are relatively far apart from each other so that the water vapor that is mixed in with the gas introduced from the gas introduction hole is less apt to adhere to the inside opening of the intake air negative pressure outlet hole. This arrangement may be difficult to achieve, however, depending on how the intake manifold is mounted.
Also, the water vapor mixed in with the gas that is introduced from the gas introduction hole may adhere to the inside surface of a wall portion that forms the surge tank and form water droplets. If these water droplets trickle down the inside surface of the wall portion and adhere to the inside opening of the intake air negative pressure outlet hole, they may freeze and block the opening.
Taking this into consideration, various ways to make inhibit the water droplets from adhering to the inside opening of the intake air negative pressure outlet hole have been devised. For example, the art disclosed in Japanese Patent Application Publication No. JP-A-2004-124831 provides a baffle plate around the intake air negative pressure outlet hole, while the art disclosed in Japanese Patent Application Publication No. JP-A-2003-254178 provides a partition wall portion in front of the intake air negative pressure outlet hole.
While the conventional examples described above may make it possible to prevent water droplets adhering to the inside surface of the wall portion that forms the surge tank from adhering to the inside opening of the intake air negative pressure outlet hole and freezing, the baffle plate and partition wall portion have comparatively complicated shapes, which means that a mold must be designed taking into account workability when opening the mold. As a result, designing the mold is difficult and increases manufacturing costs. Thus there remains room for improvement.
In addition, with a metal intake manifold, it is possible to insert a cylindrical pipe through the intake air negative pressure outlet hole in state in which it protrudes from the inside opening such that water droplets are inhibited from adhering to the inside protruding end of the cylindrical pipe. The problem with this arrangement, however, is that not only is it heavy, which goes against recent technological trends, but costs may increase due to the increase in the number of parts and assembly processes and the like.
Also, when an intake manifold such as that described above is manufactured out of resin in order to reduce both costs and weight, it is necessary in forming the protruding portion that corresponds to the cylindrical pipe described above to design a mold taking into account workability when opening the mold, which is extremely difficult to the point to which it may be considered impractical.